An embodiment relates generally to GPS-assisted positioning.
Global Positioning System (GPS) or other Global Navigation Satellite System (GNSS) receivers operate by tracking line of sight signals. These receivers typically require at least four or more satellites to be continuously available in an unobstructed line of sight of a satellite receiver on a vehicle. Due to natural and man-made obstructions (e.g., buildings) or natural obstructions (i.e., dense tree cover), the theoretical minimum number of satellites required to accurately determine a position of the satellite receiver may not be available under certain conditions. When a vehicle GPS receiver looses communication with the respective satellites due to natural or man-made obstructions, other data such as that used for dead-reckoning positioning may be used to compensate for location error increase as a result of poor GPS accuracy. Generally, GPS combined systems output a position error estimate and the higher the error, the less reliable the estimated GPS position.
Inertial or other vehicle sensors such as yaw rate sensors may be used to generate GPS aiding data. Techniques used to aid GPS are generally capable of relative navigation (capture position and orientation change with respect to a given local starting point) whereas GPS is capable of providing absolute position information with respect to a global framework. Dead Reckoning (DR) is one example of such relative navigation techniques. One drawback utilizing yaw rate measurements or data from other such sensors is that pure integration over time without corrections or calibration accumulates sensor errors such as noise and bias in the sensors where the contamination of noise and bias depends largely on the quality of a sensor. As an example, while bias and noise level of typical yaw rate sensors may not be high for a short term application, the result is that the integration of the yaw rate sensor measurements is only valid for a few tens of seconds. Integration errors due to noise and bias grow quickly as time goes forward. Therefore, the integration process needs to be either reset and initialized or updated continuously. Therefore, the aid of using yaw sensors in the location estimation and location error estimate of the GPS system can only be utilized for short durations of time as a function of the sensor quality.